1. Field of the Invention
This invention relates to a liquid natural gas filling system and, more specifically, to a natural gas filling system having a low pressure vessel for holding a bulk quantity of liquid natural gas, and a high pressure vessel, for filling a use vessel, such as a fuel tank on a vehicle.
2. Background Information
There are an increased number of vehicles that use liquid natural gas (LNG) as a fuel. As such there is an increased need for filling systems to refuel the LNG vehicles and a need for such filling systems to hold an increased amount of fuel. It is understood that the pressure and temperature of a fluid in an enclosed space are related and that a higher pressure corresponds to higher temperature and a lower pressure corresponds to a lower temperature. Hereinafter, the pressure of the LNG will be identified as “high” or “low”, it is understood that LNG at a lower pressure is also at a lower temperature. The fuel tank on an LNG vehicle is structured to hold the LNG at a pressure between about 75 psi to 125 psi. As used herein, this pressure shall be referred to as a “high” pressure. To contain the LNG, and any natural gas vapor, at such a high pressure, the LNG vehicle fuel tank is structurally robust. The manufacture of small vessels structured to contain LNG at a high pressure is not difficult or exceedingly expensive.
Presently, the filling systems for LNG vehicles include a bulk vessel that is structured to be coupled directly to the vehicle's LNG fuel tank. Because the bulk vessel is coupled directly to the fuel tank, the LNG in the bulk vessel must be maintained at a pressure similar to the pressure of the LNG fuel tank. As such, the bulk vessel must be constructed to hold a large quantity of LNG at a high pressure. Construction of such a vessel is not inexpensive. It is desirable to be able to store the bulk LNG at a lower pressure to reduce the cost of the bulk LNG vessel.
There is, therefore, a need for a LNG filling system that stores the bulk LNG at a lower pressure while delivering high pressure LNG to a vehicle.
There is a further need for a LNG filling system that stores the bulk LNG at a lower pressure while delivering high pressure LNG to a vehicle which may be used to fill multiple vehicles in rapid succession.